1. Field of the Invention
The present invention relates to an image reading device, an image forming apparatus, and an image reading method.
2. Description of the Related Art
There is a known image reading device that detects a width of a document in a main-scanning direction by using an image sensor for converting image light to an image signal, rather than using a sensor (for example, a photo interrupter) for detecting a width of a document. It is also known that an image reading device, when entering a power-saving state, causes an optical means that transmits reflected light from a document to an image sensor to move to a document-width detection position, and detects a width of a document immediately after returning from the power-saving state.
For example, Japanese Laid-open Patent Publication No. 2006-238288 discloses a document reading device including a power circuit that outputs an operating voltage to each unit of the document reading device in a standby mode and stops the output in a hibernation mode, and including an energy-saving control means that, when switching from the standby mode to the hibernation mode, locates an optical means in a document-width read position and thereafter switches to the hibernation mode.
Further, Japanese Laid-open Patent Publication No. 63-117557 discloses a document reading device that includes an initial position detecting means for detecting an initial position of an optical system, drives a driving means until the initial position detecting means detects the initial position of the optical system, reversely rotates the driving means by a predetermined number of pulses in a self-starting region of the driving means from the initial position upon detection of the initial position by the initial position detecting means, then rotates the driving means in a forward direction in the self-starting region, and stops the driving means upon detection of the initial position of the optical system by the initial position detecting means.
However, conventionally, it is difficult to move a unit including a light source and a mirror to a predetermined position in a sub-scanning direction with high precision at a high speed. For example, when an image reading device returns from a power-saving mode, because a unit including a light source and a mirror is unable to move with high precision at a high speed, even if a user sets a document, the user needs to wait until document reading operation is enabled.
In view of the above circumstances, there is a need for an image reading device, an image forming apparatus, and an image reading method capable of moving a conveying unit, which conveys at least any of a light source, a reflecting member, and a photoelectric conversion element, to a predetermined position with high precision at a high speed.